(a) Field of the Invention
The present invention relates to an apparatus for sensing and measuring a current on a power circuit and comprising a shunt element and a conductive housing connected in series therewith, the housing being dimensioned to contain a transmission circuit to measure the current flowing through the shunt and to transmit the information to a remote station.
(b) Description of the Prior Art
Reference is made to Applicant's U.S. Pat. No. 4,374,359 issued Feb. 15, 1983 to the assignee of the present application and wherein there is disclosed and claimed a co-axial shunt wherein the electronic circuitry is located in a chamber internally of the shunt. Such a structure requires that current flow in a co-axial manner in the shunt wherein the inner chamber is not subjected to the effects of the magnetic field casued by the current flow in the shunt. However, an inconvenience of such structure is that the ambient temperature in the chamber greatly increases, particularly in warm climatic conditions,and affects the proper operation of the electronic components within the circuits located in the chamber.
In standard co-axial shunts used for measuring currents of 1 kA to 100 kA or over, great care is required at the installation stage to ensure that the output voltage originates from the resistive part of the shunt and not from the strayed magnetic coupling between the measured current and the shielded conductor carrying the low voltage to the conditioning amplifier. This constitutes a basic limitation in the use of such shunts since the cable carrying the information signals has to pass by the end of the shunt close to the heavy current of the line.
For high voltage transmission line application, these types of shunts are usually mounted at the tope of an insulation column and it is desirable to control the parameters of the electronic circuits located in the shunt from a remote ground station. It is also desirable to transmit the data from the electronic circuit housed in the shunt in a form unaffected by the magnetic field effects of such shunt.